http://people.virginia.edu/~tdw/nisbett&wilson.pdf
In short, people often have no idea why they chose to do what they did. However, when asked, "why did you choose to do that?" they will rarely say, "I don't know" but will instead concoct stories that explain their choices -- explanations that are often wrong.
Teacher: What did you think about <subject>
Teen: I think it's fun
Teacher: Why do you think it's 'fun', just saying it's 'fun' is not a valid opinion.
Teen: Because it engages my curiosity and I want to learn more about <subject>
Teacher: That's good, you shou...
Later you'll hear the pupil complaining, that such exercises are pointless, because the second clarification of the pupil's opinion is just as circular and empty as the initial declaration of 'fun'. You can play this game to infinity, and you will never get to the point that any words have any real intrinsic value.
Piggybacking on SCHiM's comment, and changing "choices" to "beliefs", this is also something you will learn from looking at tribal societies (creation myths, etc).
Now I'm reminded of this clip from the Star Trek TNG episode Who Watches the Watchers (https://www.youtube.com/watch?v=Uii5WrmChbE)